This invention relates generally to hydrogen storage units and alloys. More specifically this invention relates to hydrogen storage alloys which have been atomically engineered to include a spectrum of hydrogen bonding energies and multiple hydride phases which extend and enhance their storage capacity at high pressures. The invention also includes high pressure hydrogen storage units which contain a variable amount of the hydrogen storage alloy therein to enhance the storage capacity of the unit beyond that obtainable by pressurized hydrogen gas alone.
Hydrogen is the xe2x80x9cultimate fuelxe2x80x9d for the next millennium, and, it is inexhaustible. Hydrogen is the most plentiful element in the universe and can provide an inexhaustible, clean source of energy for our planet which can be produced by various processes which split water into hydrogen and oxygen. The hydrogen can be stored and transported in solid state form.
In the past considerable attention has been given to the use of hydrogen as a fuel or fuel supplement. While the world""s oil reserves are depletable, the supply of hydrogen remains virtually unlimited. Hydrogen can be produced from coal, natural gas and other hydrocarbons, or formed by the electrolysis of water, preferably via energy from the sun which is composed mainly of hydrogen and can, itself, be thought of as a giant hydrogen xe2x80x9cfurnacexe2x80x9d. Moreover hydrogen can be produced without the use of fossil fuels, such as by the electrolysis of water using nuclear or solar energy, or any other form of economical energy (e.g., wind, waves, geothermal, etc.). Furthermore, hydrogen, is an inherently low cost fuel. Hydrogen has the highest density of energy per unit weight of any chemical fuel and is essentially non-polluting since the main by-product of xe2x80x9cburningxe2x80x9d hydrogen is water. Thus, hydrogen can be a means of solving many of the world""s energy related problems, such as climate change, pollution, strategic dependancy on oil, etc., as well as providing a means of helping developing nations.
The earliest work at atomic engineering of hydrogen storage materials is disclosed by Stanford R. Ovshinsky (one of the present inventors) in U.S. Pat. No. 4,623,597 (xe2x80x9cthe ""597 patentxe2x80x9d), the contents of which are incorporated by reference. Ovshinsky, described disordered multicomponent hydrogen storage materials for use as negative electrodes in electrochemical cells for the first time. In this patent, Ovshinsky describes how disordered materials can be tailor made to greatly increase hydrogen storage and reversibility characteristics. Such disordered materials are formed of one or more of amorphous, microcrystalline, intermediate range order, or polycrystalline (lacking long range compositional order) wherein the polycrystalline material may include one or more of topological, compositional, translational, and positional modification and disorder, which can be designed into the material. The framework of active materials of these disordered materials consist of a host matrix of one or more elements and modifiers incorporated into this host matrix. The modifiers enhance the disorder of the resulting materials and thus create a greater number and spectrum of catalytically active sites and hydrogen storage sites.
The disordered electrode materials of the ""597 patent were formed from lightweight, low cost elements by any number of techniques, which assured formation of primarily non-equilibrium metastable phases resulting in the high energy and power densities and low cost. The resulting low cost, high energy density disordered material allowed such Ovonic batteries to be utilized most advantageously as secondary batteries, but also as primary batteries and are used today worldwide under license from the assignee of the subject invention.
Tailoring of the local structural and chemical order of the materials of the ""597 patent was of great importance to achieve the desired characteristics. The improved characteristics of the anodes of the ""597 patent were accomplished by manipulating the local chemical order and hence the local structural order by the incorporation of selected modifier elements into a host matrix to create a desired disordered material. The disordered material had the desired electronic configurations which resulted in a large number of active sites. The nature and number of storage sites was designed independently from the catalytically active sites.
Multiorbital modifiers, for example transition elements, provided a greatly increased number of storage sites due to various bonding configurations available, thus resulting in an increase in energy density. The technique of modification especially provides non-equilibrium materials having varying degrees of disorder provided unique bonding configurations, orbital overlap and hence a spectrum of bonding sites. Due to the different degrees of orbital overlap and the disordered structure, an insignificant amount of structural rearrangement occurs during charge/discharge cycles or rest periods therebetween resulting in long cycle and shelf life.
The improved battery of the ""597 patent included electrode materials having tailor-made local chemical environments which were designed to yield high electrochemical charging and discharging efficiency and high electrical charge output. The manipulation of the local chemical environment of the materials was made possible by utilization of a host matrix which could, in accordance with the ""597 patent, be chemically modified with other elements to create a greatly increased density of catalytically active sites for hydrogen dissociation and also of hydrogen storage sites.
The disordered materials of the ""597 patent were designed to have unusual electronic configurations, which resulted from the varying 3-dimensional interactions of constituent atoms and their various orbitals. The disorder came from compositional, positional and translational relationships of atoms. Selected elements were utilized to further modify the disorder by their interaction with these orbitals so as to create the desired local chemical environments.
The internal topology that was generated by these configurations also allowed for selective diffusion of atoms and ions. The invention that was described in the ""597 patent made these materials ideal for the specified use since one could independently control the type and number of catalytically active and storage sites. All of the aforementioned properties made not only an important quantitative difference, but qualitatively changed the materials so that unique new materials ensued.
The disorder described in the ""597 patent can be of an atomic nature in the form of compositional or configurational disorder provided throughout the bulk of the material or in numerous regions of the material. The disorder also can be introduced into the host matrix by creating microscopic phases within the material which mimic the compositional or configurational disorder at the atomic level by virtue of the relationship of one phase to another. For example, disordered materials can be created by introducing microscopic regions of a different kind or kinds of crystalline phases, or by introducing regions of an amorphous phase or phases, or by introducing regions of an amorphous phase or phases in addition to regions of a crystalline phase or phases. The interfaces between these various phases can provide surfaces which are rich in local chemical environments which provide numerous desirable sites for electrochemical hydrogen storage.
These same principles can be applied within a single structural phase. For example, compositional disorder is introduced into the material which can radically alter the material in a planned manner to achieve important improved and unique results, using the Ovshinsky principles of disorder on an atomic or microscopic scale.
One advantage of the disordered materials of the ""597 patent were their resistance to poisoning. Another advantage was their ability to be modified in a substantially continuous range of varying percentages of modifier elements. This ability allows the host matrix to be manipulated by modifiers to tailor-make or engineer hydrogen storage materials with all the desirable characteristics, i.e., high charging/discharging efficiency, high degree of reversibility, high electrical efficiency, long cycle life, high density energy storage, no poisoning and minimal structural change.
Until the advent of the instant invention, no one has applied Ovshinsky""s atomic engineering principals to provide low temperature hydrogen storage alloys that have extended storage capacity at higher pressures. Thus there remains a compelling and crucial need in the art for low temperature alloys which have extended storage capacity at higher pressures to thereby provide safe, efficient, reliable, cost effective alloys storing and delivering large quantities. The instant alloys and storage units in which they are used are made possible by the application of Ovshinsky""s principles of atomic engineering, which create alloys having a spectrum of hydrogen bonding energies and multiple hydride phases.
The objects of the instant invention include a solid state hydrogen storage unit which includes a pressure containment vessel having at least one hydrogen inlet/outlet port for transferring hydrogen into and out of the vessel and a hydrogen storage alloy disposed with the containment vessel. The hydrogen storage alloy being in sufficient quantity to provide for bulk storage of hydrogen and having a storage capacity at ambient temperatures and at a pressure of at least two times the plateau endpoint pressure of at least 10% higher than the storage capacity of said alloy at the same temperature and at the plateau endpoint pressure.
More preferably, the hydrogen storage alloy has a storage capacity at ambient temperatures and at a pressure of at least three times the plateau endpoint pressure of at least 15% higher than the storage capacity of the alloy at the same temperature and at the plateau endpoint pressure. Even more preferred are alloys which have a storage capacity at ambient temperatures and at a pressure of at least four times the plateau endpoint pressure of at least 20% higher than the storage capacity of the alloy at the same temperature and at the plateau endpoint pressure. More preferred yet are alloys which have a storage capacity at ambient temperatures and at a pressure of at least five times the plateau endpoint pressure of at least 23% higher than the storage capacity of the alloy at the same temperature and at the plateau endpoint pressure. Most preferred are alloys which have a storage capacity at ambient temperatures and at a pressure of at least six times the plateau endpoint pressure of at least 25% higher than the storage capacity of the alloy at the same temperature and at the plateau endpoint pressure.
In an alternative embodiment, hydrogen storage alloy has a high pressure extended storage capacity slope of less than 5 at ambient temperature but greater than the slope of the plateau pressure capacity at the same temperature. More preferred alloys have a high pressure extended storage capacity curve slope of less than 4.5 at ambient temperature but greater than the slope of the plateau pressure capacity curve at the same temperature. Even more preferred alloys have a high pressure extended storage capacity curve slope of less than 4 at ambient temperature but greater than the slope of the plateau pressure capacity curve at the same temperature. Yet further preferred alloys are those which have a high pressure extended storage capacity curve slope of less than 3.5 at ambient temperature but greater than the slope of the plateau pressure capacity curve at the same temperature. Finally, most preferred alloys are those which have a high pressure extended storage capacity curve slope of less than 3 at ambient temperature but greater than the slope of the plateau pressure capacity curve at the same temperature.
Specifically the hydrogen storage alloy is an alloy is an AB2 alloy, such as a modified Tixe2x80x94Mn2 alloy comprising, in atomic percent 2-5% Zr, 26-33% Ti, 7-13% V, 8-20% Cr, 36-42% Mn; and at least one element selected from the group consisting of 1-6% Ni, 2-6% Fe and 0.1-2% Al. The alloy may further contain up to 1 atomic percent Misch metal. Examples of such alloys include in atomic percent: 1) 3.63% Zr, 29.8% Ti, 8.82% V, 9.85% Cr, 39.5% Mn, 2.0% Ni, 5.0% Fe, 1.0% Al, and 0.4% Misch metal; 2) 3.6% Zr, 29.0% Ti, 8.9% V, 10.1% Cr, 40.1% Mn, 2.0% Ni, 5.1% Fe, and 1.2% Al; 3) 3.6% Zr, 28.3% Ti, 8.8% V, 10.0% Cr, 40.7% Mn, 1.9% Ni, 5.1% Fe, and 1.6% Al; and 4) 1% Zr, 33% Ti, 12.54% V, 15% Cr, 36% Mn, 2.25% Fe, and 0.21% Al.
The storage unit may further include a thermal management system for alternately cooling and heating said hydrogen storage alloy during charge and discharge thereof, respectively. The storage unity may also include means to divide the interior of the pressure vessel into compartments. The means to divide the interior of the pressure vessel into compartments may be selected from honeycomb structures, metal foam, disk dividers, screens, pinwheel dividers and combinations thereof.